Method of recovering the solids from pulp mill waste liquors



Dec., 5,` 1939., E FLADMARK 2,182,428

METHOD' 0F RECOVERING THE soLIDs FROM PULP MILL WASTE LIQUORS Filed NOV. l1, 1955 Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE METHOD OF RECOVERING THE SOLIDS FROM PULP MILL WASTE LIQUORS 1 Claim.

This invention relates to the evaporation of liquids containing solids in solution and/or suspension for the purpose of separating the former from the latter, and it has for its object to pro- 5 vide a commercial process for economically and expeditiously separating and segregating f the solids andthe liquids through evaporation of the latter.

It is also the object of this invention to effect the evaporation of water containing a solid or solids in solution and/or suspension so that said water is continuously converted into steam while all of the solid matter is simultaneously and continuously separated from the water and steam in a bone dry, or nearly bone dry condition. By the expression bone dry I mean the total absence of Water irrespective of any other physical condition or characteristic of the solid matter.

It is also one of the objects of this invention to recover the solids from industrial waste liquors under such conditions that all of the water in such waste liquors is separated therefrom, while the solids are simultaneously recovered in a practically bone dry condition.

An example is pulpmill waste liquors. In the operation of pulp mills there are large quantities of waste liquors to be disposed of which contain about ten per cent useful organic and inorganic compounds in solution. In the pulping processes known as the sulphate process and the soda process these liquors are evaporated and incinerated in order to recover the valuable sodium salts which they contain.

The waste liquor from the pulping process` known as the s11lphit e process does not contain any such valuable salts and therefore the disposal of this liquor by evaporation and incineration has not heretofore been economical but,

on the contrary, a matter of expense and was resorted to merely as a means of disposal in localities Where legislation prohibits the dumping of large quantities Aof waste liquors into rivers or other waters. It is one of the objects of this invention to provide an economical and profitable of this kind.

The evaporation of the waste liquors above referred to has heretofore commonly been carried out in multiple effect evaporators under comparatively low pressure and owing to the high viscosity of the concentrated waste liquors the maximum concentration obtainable was only in the neighborhood of fifty or sixty percent.

Another dimculty, particularly troublesome Vwhen sulphite waste liquor is evaporated, is the method of recovering the solids from waste liquor p connected by a pipe conduit I I with a downwardly directed spray nozzle I2 disposed within, and at the top of, an evaporator I3 whose lower part contains a heat transfer medium I4. In the pipe conduit II is arranged a continuously driven pump I6 by which the liquor is pumped from the storage tank to nozzle I2. The heat transfer medium Id is a liquid, or a solid compound that is liquid at the normal operating temperature. This heat medium may be an oil, tar, pitch, asphalt, wax or other suitable compound, and its function is to transfer heat from a heater I5 to the liquor to be evaporated that is discharged by nozzle I2 and also to remove from the evaporator I3 the solid residue. Any compound that is liquid at the normal operating temperature; that is non-volatile. at said temperature, and which does not enter into chemical reactions with the liquor being treated may be used as this heat transfer medium, and it should therefore be understood that I do not intend to limit myself to the few examples given above.

The transfer medium It is heated by the heater I5 well above the boiling temperature of the liquid to be evaporated and while I prefer a temperature of degrees C., so that all the water in the solution may be rapidly driven off as steam when the spray hits the top surface of the transfer medium III, it will be clear that a higher or a lower temperature may be employed so long as all of the water is released as steam while practically nothing of the heat transfer medium I is evaporated. This determines the lower temperature limit at or slightly above the boiling point of the solution to be evaporated, and the upper limit at or slightly below the boiling pointv of the heat transfer medium I4 at the pressure maintained in the apparatus. Within these limits the temperature vmay be varied as desired.

The steam evolved in the evaporator vI3 is drawn off through an outlet pipe I'I for use, said 55 outlet pipe being connected with the upper part of the interior of the evaporator I3.

The conversion of the water of the liquor into steam within the evaporator I3 leaves the solid residue as a suspension in the heat transfer medium.

The bottom of the interior of evaporator I3 is connected by a pipe conduit I8 with the inlet of a separator I9 within which the absorbed or entrained solids are removed from the transfer medium, the latter being returned to the evaporator I3 through a pipe conduit 20 provided. with a pump 2I and also with a coil 22 forming part of heater I5. The pump 2| operates to continuously circulate the transfer medium through coil 22, evaporator I3 and separator I9, the latter being constructed with a filter, centrifuge or some other suitable means for removing the solids from the transfer medium.

Heat transfer medium removed with the solids may be returned or replaced within the apparatus through a normally closed inlet conduit 23.

The solid residue lsolatedby separator I9 is removed from the latter through an outlet 24,' and said residue is now practically free from moisture but saturated with heat transfer medium I4. The amount of heat transfer medium found with the solids may be as great as 100% of their weight depending on the method of separation.

It should be understood, of course, that I have hereinabove indicated a separator I9 only as an example of one Apractical and possible means for removing the solids from the heat transfer medium and that in the broader aspect of the invention this separating operation or step is not essential since the suspension as it comes from the evaporator may nd commercial application.

What I claim is:

The method of recovering the solids from pulp mill waste liquors which consists in continuously spraying the liquor against the surface of a body of heated liquid heat transfer medium within an evaporator at such a rate of i'low that the water of said waste liquor is evaporated upon contact with said surface before the Waste liquor and liquid heat transfer medium can mix while the solid residue of said waste liquor is being continuously absorbed in dry condition by the liquid heat transfer medium and continuously removed from the evaporator with the latter.

A ERLING FLADMARK. 

